There are well known devices for air humidification by evaporating water. It has been contemplated as well to use finely atomized water droplets for decentralized air humidification (16. Status-Seminar “Forschen und Bauen im Kontext von Energie und Umwelt”, 2./3. September 2010, Ch. Vogel, Dr. A. Grüniger, Dr. B. Wellig, “Ein behagliches Raumklima durch direkte adiabate Raumluftbefeuchtung mit Tropfen (DART)”). However, this concept has so far not been used in practical installations fit for every-day use. WO 2008/100077 A1 shows a humidifier to be built-in and in connection with a water pipe of a building. This humidifier uses a piezoceramic vibrator at the bottom of a reservoir and provides for atomized water rising from the reservoir and being discharged above the reservoir. For preventing germs when the humidifier stops and a predetermined amount of water remains in the reservoir, a drier is suggested for removing water in the reservoir. WO 2010/015124 A1 shows another humidifier with a reservoir, an ultrasonic transducer at the bottom of the reservoir and a mist guiding duct extending upwardly from the reservoir. US 2002/0163090 A1 and JP 2006292249 A show humidifiers as well.